From 208278a116710606095215db716ec2e1c99855cb Mon Sep 17 00:00:00 2001
From: Brett Parker <iDunno@sommitrealweird.co.uk>
Date: Tue, 8 Dec 2020 21:12:21 +0000
Subject: [PATCH 1/1] More optimisation for day10

---
 day10/check_asteroids.sh | 81 +++++++++++++++++++++++-----------------
 1 file changed, 46 insertions(+), 35 deletions(-)

diff --git a/day10/check_asteroids.sh b/day10/check_asteroids.sh
index 8faf834..bf54544 100755
--- a/day10/check_asteroids.sh
+++ b/day10/check_asteroids.sh
@@ -115,50 +115,61 @@ fast_checks() {
     start_x=${asteroid%,*}
     start_y=${asteroid#*,}
 
-    hitblocker=0
-
     max_x=$width
     max_y=$ln
 
-    # first, head left of the asteroid
-    for (( x=$((start_x-1)); x>=0; x-- )); do
-        do_blocker_check $asteroid $x $start_y
+    # directions:
+    # -1, 0 - left
+    #  1, 0 - right
+    #  0, 1 - up
+    #  0,-1 - down
+    # -1, 1 - diagonal left down
+    # -1,-1 - diagonal left up
+    #  1, 1 - diagonal right down
+    #  1,-1 - diagonal right up
+    for direction in -1,0 1,0 0,1 0,-1 -1,1 -1,-1 1,1 1,-1; do
+    #for direction in "-1,0" "1,0" "0,1" "0,-1"; do
+        stepx=${direction%,*}
+        stepy=${direction#*,}
+        do_blocker_check $start_x $start_y $stepx $stepy
     done
-    hitblocker=0 # this gets updated in do_blocker_check, reset it
+}
 
-    # now head right of the asteroid
-    for (( x=$(($start_x+1)); x<= $width; x++ )); do
-        do_blocker_check $asteroid $x $start_y
-    done
-    hitblocker=0 # this gets updated in do_blocker_check, reset it
+do_blocker_check() {
+    startx=$1
+    starty=$2
+    stepx=$3
+    stepy=$4
 
-    # head upwards
-    for (( y=$((start_y-1)); y>=0; y-- )); do
-        do_blocker_check $asteroid $start_x $y
-    done
-    hitblocker=0 # this gets updated in do_blocker_check, reset it
+    hitblocker=0
 
-    # head down
-    for (( y=$((start_y+1)); y<=$ln; y++  )); do
-        do_blocker_check $asteroid $start_x $y
-    done
-}
+    if [ $stepx -eq 0 -a $stepy -eq 0 ]; then
+        echo "Somehow got 0 and 0 as steps"
+        return
+    fi
 
-do_blocker_check() {
-    asteroid=$1
-    x=$2
-    y=$3
-
-    if [ ${asteroids[$x,$y]+a} ]; then
-        if [ $hitblocker -eq 0 ]; then
-            cansee[$asteroid,$x,$y]=1
-            cansee[$x,$y,$asteroid]=1
-            hitblocker=1
-        else
-            cantsee[$asteroid,$x,$y]=1
-            cantsee[$x,$y,$asteroid]=1
+    local x=$startx
+    local y=$starty
+
+    # add the steps before we start the loop to not be
+    # on ourselves
+    x=$((x+$stepx))
+    y=$((y+$stepy))
+
+    while [ $x -le $width -a $x -ge 0 -a $y -le $ln -a $y -ge 0 ]; do
+        if [ ${asteroids[$x,$y]+a} ]; then
+            if [ $hitblocker -eq 0 ]; then
+                cansee[$asteroid,$x,$y]=1
+                cansee[$x,$y,$startx,$starty]=1
+                hitblocker=1
+            else
+                cantsee[$startx,$starty,$x,$y]=1
+                cantsee[$x,$y,$startx,$starty]=1
+            fi
         fi
-    fi
+        x=$((x+$stepx))
+        y=$((y+$stepy))
+    done
 }
 
 possibly_in_way() {
-- 
2.39.5